Insertional mutagenesis of MoMuLV induced T cell lymphoma lines is a powerful genetic tool that can be used to identify genes associated with selectable phenotypes. Preliminary studies leading to this proposal explored the use of two alternative insertional mutagenesis strategies to isolate interleukin-2 (IL-2) independent mutants of three IL-2 dependent T cell lymphoma lines. Two genes involved in the progression to IL-2 independence (Gfi and Gfi-2, growth factor independence-1 and 2) were identified using these strategies. Gfi-1 encodes a protein with six zinc finger motifs whose expression is restricted to lymphoid tissues and testis in adult animals. During mitogen induced T cell activation, Gfi-1 induction occurs after IL-2/IL-2R interaction, during the period preceding T cell proliferation. Gfi-2 expression is restricted to the thymus and spleen. During T cell activation, induction of Gfi-2 appears to follow induction of Gfi-1. The experiments described in this proposal were designed to determine the role of Gfi-1 and Gfi-2 in the regulation of T cell proliferation. A set of lower priority experiments will also address the nature of additional genes presumed to be involved in the transition of T cell lymphoma lines to IL-2 independence. Since the release of tumor cells from their dependence on IL-2 is likely to be associated with an enhancement of their malignant potential, the genes associated with the transition to IL-2 independence may also be involved in tumor progression. To achieve the goals of this application we will utilize recombinant DNA and tissue culture technologies. Animal experiments will include the inoculation of immunocompromised mice and syngeneic rats with tumor cells and the inoculation of newborn rats and mice with recombinant retroviruses.